The prior art is filled with a variety of cutting tools of different designs and compositional make-up. Various types of diamond compositions have been used to improve the cutting ability and wear of such tools. The most common type of diamond used in cutting tools is a diamond compact. Diamond compacts are a mixture of a binder, such as cobalt, and diamond powder. Such diamond compact materials are relatively thick, e.g. about 0.080" (2.03 mm), and relatively short in length, e.g. about 0.065" (1.65 mm) maximum. To install such diamond compacts in flutes of, for example, an end mill, it is necessary to remove a significant amount of the tool base material that forms the flute, so as to form a pocket (channel) for the insertion of the diamond compact. As a result of the removal of the tool base material from the flute, the flute is weakened. To produce a tool with a shear angle of greater than 0.degree., the flute must be angled, which requires cutting away even more of the flute material. The combination of the channeling of the flute to accommodate the diamond compact and the angling of the flute to create a shear angle weakens the tool and renders it incapable of being used in high shear applications. Moreover, the diamond compact contains cobalt which may react with the tool base material and cause the diamond compact to become overheated and wear away during use. As a result, a diamond end mill has never been successfully marketed on a large scale.
In one attempt to solve this problem, a fluted rotary tool of cemented carbide in which the cutting part is coated with a thin layer of polycrystalline diamond by a vapor phase synthetic method has been developed. The problem with this approach is that the adhesiveness between the cemented carbide and the diamond film has not proven to be sufficient to prevent stripping of the diamond film during use.
U.S. Pat. No. 5,070,748 discloses helical fluted tools which are a two-piece construction, i.e. the cutting portion is formed by electrical discharge machining (EDM) followed by packing in a polycrystalline diamond complex and hot isostatic pressing to hold the complex in position. This blank is then ground to the desired finish geometry and brazed by standard technology to a tungsten carbide shank which has been ground concentric thereto. A major problem in this tool is that the braze is being relied upon to absorb all the forces involved in cutting, and the braze cannot and does not hold up. In fact, in tests of tools prepared in accordance with this patent in composite machining applications, the tools failed very prematurely due to braze failure. Also, in the composite machining, the helix delaminated the composite material in the direction of the helix--an unacceptable result.
U.S. Pat. No. 5,020,394 discloses yet another method to overcome the problem encountered by the prior art tools. The tool is produced by forming, by a vapor phase synthesis method, a polycrystalline diamond film on the surface of a substrate which has been subjected to helical grinding; then subjecting the product to chemical treatment to remove only the substrate, brazing the resulting diamond film in a fluted form to at least a part of the rake face of a tool base metal and then subjecting the brazed tool base metal to working of a flank face to form a cutting edge. The tools produced are very expensive due to the complex technology required and furthermore a two-step brazing process is used which is both expensive and results in a poor quality bond.
Accordingly, it is an object of the present invention to construct a fluted cutting tool with a diamond cutting surface that is durable and inexpensive to manufacture.
It is another object of the present invention to construct a fluted cutting tool with a diamond cutting surface that has a cutting surface having a radial rake of greater than 0.degree., the radial rake angle being the angle between the rake face and a radius from the rotational axis of the tool to the cutting edge.
It is another object of the present invention to construct a fluted cutting tool in which the radial rake angle can be readily adjusted.